Ever hear someone say that every human has cancer at a given moment in time? Although clinically undetected cancers are common, the natural defenses of your body often eliminate abnormal cells before a cancerous disease state occurs.

A number of genetic failures are necessary before unbridled replication begins. We will address the genetic fail-safes forestalling cancer, the path of these replicating cells as they make their way through the body, and the immune response to these untethered cells.
The top image shows a single necrotic tumor cell in the center of a squamous carcinoma. Image by The Armed Forces Institute of Pathology and is held within the public domain.

Historical views of cancer
Cancer is not a new disease. A text within the Edwin Smith Papyrus describes the removal of several growths from Egyptian patients in 1600 BCE. The text mentions the use of a "fire drill" a to remove growths that lack a treatment, with these growths matching descriptions of modern tumors.

In the 16th Century CE, physicians believed cancer to be contagious, leading to the isolation of breast cancer patients from the rest of society. Prior to adoption of our current cellular understand of cancer, physicians theorized that cancer developed from prior physical trauma. Physicians, however, lacked the ability to link physical trauma inflicted on animals in experiments to cancerous growths later in their life.

90 trillion cells
An adult human is comprised of anywhere from sixty to ninety trillion cells. Odds are, out of the 90,000,000,000,000 cells in your body, you going to have a few rogue ones, ones that will be replicating uncontrollably at any one time.

Cells are meant to die and be replaced by new ones - skin cells are sloughed off and replaced by soft, shiny new members of your body. Cellular replication is a natural process, as long as it leads to a proper cell lifespan and replication rate. Proper replication stems from a delicate cascade of cell signaling steps taking into account the availability of nutrients and growth factors. A chain reaction of errors, however, in genetic quality and cell signalling lead to the unwarranted replication of cells and eventual tumor growth.

Tumor suppressor genes yield proteins that cause cellular suicide at the appropriate time or prevent replication of cells with damaged DNA, while a buildup of mutations in tumor suppressor genes can lead to cells growing to an inappropriate age. Mutations also play a role in cellular replication, as mutation and activation of oncogenes in the body can lead to the uncontrolled replication of cells and possibly tumor growth.

Too many mutations
A buildup of genetic mutations can arise for a variety (and often a combination) of reasons, from environmental cues to exposure to hazardous chemicals (like bezene) or radiation while working. These mutations, if not dealt with by the body, continue to accumulate through life, making cancerous growths more prevalent as one ages.

As the average human lifespan increases, so will the number of accumulated genetic mutations. Mutations leading to cancer will continue to pose a problem as our lifespans approach 150 years or more by the end of the century. If we want to live comfortably well into our mid 100s, manipulating these genetic precursors to cancer will become necessary.

From replicating cell to tumor
Tumors are simply a group of rapidly replicating cells assembled in sufficient quantities to form a distinct tissue. When replicating cells accumulate, the cells can forcefully push through tissue and invade nearby organs. Cells leading to cancerous tumors also create a variety of proteins that degrade surrounding tissue, causing a decrease in organ efficiency. In the process, these cells physically change on the outside, with antigens often dotting their surface — antigens that can warn the body's immune system.

Additional trouble begins when cancer cells separate and move through the blood stream, although many cells will not survive the harsh journey out of the bloodstream and onto another organ. Cells leading to cancer can also move through the lymphatic system, posing a problem when the cells gather and replicate around lymph nodes.

When the opportunity to accumulate on another organ and replicate arises, the cells often end up in the vicinity of the liver, lungs, or bone, creating a secondary cancer. For instance, pancreatic cells can replicate, travel, and grow tumors within the liver. Once on the liver, the pancreatic cells initiate a re-routing the liver's blood supply, stealing nutrients and disrupting the organ's ability to operate at an optimum level. Cancerous growths that arise on bone can be particularly painful, but the pain doubles as a symptom that might lead one to seek treatment. Routine blood tests might tip a physician off to cancer, as a blood test could detect an abnormal immune response activity or antigens commonly associated as tumor markers.

A part of cancer diagnosis is establishing the "grade" of the tumor. The grade is a measure of how closely the cells making up the tumor resemble the cells of the tissue they originated from. As the cells in the tumor become less like their original cells, a higher grade is given to the tumor — cells akin to undifferentiated cells (and no longer resembling their parent tissue) lead to a poor patient prognosis.

Immunosurveillance
These quickly replicating cells can be virtually indiscernible by clinical means, providing time for accumulation and the onset of symptons or for one's immune system to counteract the growth. Time, chance, and immune response are often the difference between an undiagnosable presence of cancerous cells in the body and living with cancer as a disease state.

Tiny accumulations of uncontrolled cell growth are attacked and disrupted by your body's immune system (particularly lymphocytes like B cells, natural killer cells, and T cells), but once this cellular mass grows to a diagnosable and organ impairing size, cancer, as a disease state, begins. Often these cellular growths are not detected by the immune system until it is too late, leading to substantial tumor growth and surgery and/or chemotherapy.

I know you hear it all the time, but if you want to live well into your 150s and experience all of the glories of our 22nd Century future, check for lumps regularly and get a physical every year or two. A few minutes of discomfort could add years to your life — years you could spend getting cybernetic implants, being disappointed by the fourteenth Alien film, vacationing on Mars, and finally seeing the inevitable remake of A New Hope.